Dynamic stability of helical and barrel coils in transformers against axial short - circuit forces

The axial instability of winding conductors is one of the frequent modes of short-circuit failures in power transformers. This paper throws a new light on this failure mode for helical and barrel coils and takes important steps forward in three ways: (i) recognising a new mode of possible failure. (ii) accounting for the dynamic considerations leading to the formula for calculating the mechanical resonance frequency which one must avoid in the design. (iii) calculating the critical strength of winding conductors which should not be exceeded. The conclusions here will help the design engineer to keep the transformer windings stable under short-circuit forces.